Custom designed Dummy Loads for HV Pulsed Power Modulator Testing

Michael Osemann, Carsten Rediess

Ampegon PPT GmbH, Feldstrasse 56, 44141 Dortmund, Germany

© Copyright 2016 Ampegon AG. All rights reserved.

As a manufacturer for industrial, medical and scientific pulsed power applications we are frequently confronted with testing new, custom designed power modulators, i.e. pulse generators. In the purposed applications these modulators are often intended to be used on extremely expensive RF tubes like Klystrons. Therefore, it became necessary for us as well as for our customers to develop corresponding dummy loads to avoid testing modulators on these expensive devices directly.

In order to test the modulators in accordance with the actual operating parameters (Upeak < 150 kV; Ipeak < 150 A; PAV < 160 kW), the dummy loads need to fulfill the same power requirements as the intended Klystrons. Although the Klystron’s perveance is not linear and furthermore depends on the applied voltage, it is sufficient to use resistive loads as a dummy. However, such a replacement load requires an appropriate high voltage, cooling and safety design.

Our basic idea was to create a modular dummy solution which can be matched easily to certain load specifications. Each module was designed as a 40 kW average power, water cooled high voltage resistive load, based on commonly used standard power resistors. Depending on the specific application up to four modules can be connected in parallel or series. For protection against high voltage the full dummy was put into a surrounding grounded cage which also contains a manifold for deionized water distribution.

At first those kind of high power dummy loads were used for factory and site acceptance tests. By time those dummies also became attractive for our customers to drive long term tests on new modulator principles or to test new purchased modulators on site.

Abstract

Dummy Load Specifications

Mobile Test Load

120 kW, 10 kV Dummy Load Pulse Voltage 10 kV Pulse Current 1600 A RMS Current 138 A Average Power 120 kW Insulation Level 18 kV Load Resistance 6.25 Ω Stray Inductance 150 µH Repetition Rate 5 Hz Duty Cycle 0.75 % Water Flow 120 l/min

Klystron Replacement Dummy at Modulator Commissioning Site

Klystron Dummy Specifications 161 kW, 115 kV Klystron Pulse Energy Input per 2.8 ms Pulse 8050 J at 20 Hz Pulse Rise Time 0.30 ms Average Power Input per Element 0.84 kW Total Average Power Input 161 kW Total Dummy Resistance 4600 Ω Pulse Voltage -115 kV at 2.8 ms / 20 Hz Water Flow for 160 kW Power Input 4 x 80 l/min VE- Water Flow (Total) 320 l/min = 19 m³/h Tin / Tout < 20°C / < 35°C Maximum Temperature Difference 15°C Differential working pressure 6 bar @ 35°C

Dummy Load Circuit Diagram Principle

Low Voltag Dummy Load Specifications

30 kW, 5 kV Dummy Load Pulse Current 190 A Average Power 30 kW Insulation Level 5 kV Load Resistance 5.14 Ω Water Flow 10 l/min

Low Voltage Test Load

Three Resistor Modules in HV Housing FAT Measurements at full -115 kV Test Voltage